5. The dual-band antenna of claim 3, wherein the spiral antenna is a
high-frequency (HF) band antenna.

6. The dual-band antenna of claim 5, wherein the spiral antenna has a
resonance frequency of 13.56 MHz.

7. The dual-band antenna of claim 5, further comprising:a non-conducting
carrier with a top side and a bottom side;metallizations on the top side
of the carrier; andmetallizations on the bottom side of the carrier.

8. The dual-band antenna of claim 7, wherein the carrier has a thickness
smaller than 100 μm.

10. The dual-band antenna of claim 7, wherein the shorted loop slot
antenna comprises an outer ring and a plate surrounded by the outer ring
to form a loop slot in the metallizations on the top side of the carrier.

11. The dual-band antenna of claim 10, further comprising a short
electrically connecting the outer ring to the plate.

12. The dual-band antenna of claim 10, wherein the plate and the outer
ring are electrically connected.

13. The dual-band antenna of claim 12, wherein the plate comprises a
cut-out to form an inner ring.

14. The dual-band antenna of claim 13, wherein a bypass strip couples a
side of the inner ring to an opposite side of the inner ring.

15. The dual-band antenna of claim 14, wherein the bypass strip is coupled
by capacitors which conduct at ultra-high-frequencies (UHF) and do not
conduct at high-frequencies (HF), the capacitors comprising a first
metallization on the bottom side of the carrier which extends at least
over the metallization of one side of the inner ring to the metallization
of the opposite side of the inner ring.

16. The dual-band antenna of claim 15, wherein the inner ring comprises a
non-conducting gap cutting through the inner ring.

17. The dual-band antenna of claim 16, further comprising a second
metallization on the bottom side of the carrier which extends at least
across the non-conducting gap in the inner ring,wherein the second
metallization, the carrier and the metallization on each side of the
non-conducting gap in the inner ring form two capacitors, each having a
capacitance so that ultra-high-frequencies (UHF) are conducted and
high-frequencies (HF) are not conducted across the gap in the inner ring.

18. The dual-band antenna of claim 17, wherein the outer ring comprises a
non-conducting gap cutting through the outer ring.

19. The dual-band antenna of claim 18, further comprising a third
metallization on the bottom side of the carrier which extends at least
across the non-conducting gap in the outer ring,wherein the third
metallization, the carrier and the metallization on each side of the gap
in the outer ring form two capacitors, each having a capacitance so that
ultra-high-frequencies (UHF) are conducted and high-frequencies (HF) are
not conducted across the gap in the outer ring.

20. The dual-band antenna of claim 19, wherein the resonance frequency of
the shorted loop slot antenna is determined by a loop slot length.

21. The dual-band antenna of claim 19, wherein the input impedance of the
shorted loop slot antenna is determined by a loop slot length.

22. The dual-band antenna of claim 19, wherein the input impedance of the
shorted loop slot antenna is determined by a feed position along the loop
slot.

23. The dual-band antenna of claim 22, wherein the input impedance of the
shorted loop slot antenna is determined by a width of the loop slot.

24. The dual-band antenna of claim 19, wherein the spiral antenna is
formed in the metallization on the top side of the carrier andcomprises
turns of conductor arranged around the outer ring of the shorted loop
slot antenna, orcomprises turns of conductor arranged inside the inner
ring of the shorted loop slot antenna.

25. The dual-band antenna of claim 24, wherein additional turns of
conductor for the spiral antenna comprise the outer ring and the inner
ring of the shorted loop slot antenna.

26. The dual-band antenna of claim 24, wherein the resonance frequency of
the spiral antenna is determined by the number of conductor turns of the
spiral antenna.

27. The dual-band antenna of claim 26, further comprising fourth and fifth
metallizations on the bottom side of the carrier for altering the
capacitance of the spiral antenna to tune the center frequency of the
spiral antenna.

28. The dual-band antenna of claim 24, wherein a quality factor of the
spiral antenna is determined by the conductor width of its conductor
turns.

29. The dual-band antenna of claim 1, wherein an electronic chip is
coupled in parallel to the shorted loop slot antenna and spiral antenna.

30. The dual-band antenna of claim 29, wherein the electronic chip is
coupled to the inner ring and the outer ring.

31. The dual-band antenna of claim 30, wherein the electronic chip is
electrically connected to sixth and seventh metallizations on the bottom
side of the carrier.

32. The dual-band antenna of claim 31, further comprising:a non-conducting
carrier with a top side and a bottom side,wherein the shorted loop slot
antenna comprises an outer ring and a plate surrounded by the outer ring,
and the plate comprises a cut-out to form an inner ring;a first
metallization on the bottom side of the carrier which extends at least
over metallization of one side of the inner ring to metallization of the
opposite side of the inner ring;a second metallization on the bottom side
of the carrier which extends at least across a non-conducting gap in the
inner ring; andfourth and fifth metallizations on the bottom side of the
carrier for altering the capacitance of the spiral antenna to tune the
center frequency of the spiral antenna,wherein the first metallization,
the second metallization, the fourth metallization and the sixth
metallization are electrically connected.

33. The dual-band antenna of claim 32, further comprising a third
metallization on the bottom side of the carrier which extends at least
across a nonconducting gap in the outer ring,wherein the third
metallization, the fifth metallization and the seventh metallization are
electrically connected.

34. The dual-band antenna of claim 33, wherein the electronic chip is
electrically connected to the inner ring by means of a first via.

35. The dual-band antenna of claim 34, wherein the electronic chip is
electrically connected to an outermost turn of the spiral antenna by
means of a second via.

36. The dual-band antenna of claim 24, wherein at least one of the inner
ring, the outer ring and the turns of conductors have a rectangular,
circular or elliptical shape.

38. The contactless data storage medium of claim 37, wherein the
contactless data storage medium is a radio frequency identification tag
or a smart card.

39. A dual-band antenna, comprising:a shorted loop slot antenna comprising
an inner ring and an outer ring, each ring comprising a non-conducting
gap;a spiral antenna comprising a plurality of conductor turns arranged
around the outer ring of the shorted loop slot antenna or comprising a
plurality of conductor turns arranged inside the inner ring of the
shorted loop slot antenna; anda switch connected to the shorted loop slot
antenna and the spiral antenna such thatat a UHF frequency the gaps of
inner ring and the outer ring are electrically shorted, andat a HF
frequency the inner ring and the outer ring are connected in series to
each other and in series to the plurality of conductor turns of the
spiral antenna.

40. The antenna of claim 39, wherein the switch comprises capacitors
conducting at the UHF frequency and non-conducting at the HF frequency.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to a dual-band antenna.

BACKGROUND OF THE INVENTION

[0002]Dual-band antennas allow the use of frequencies in different bands.
In contactless data storage media, such as radio frequency identification
(RFID) tags, different frequency bands can be used to achieve optimum
operation under different ambient conditions. Frequencies in the
ultra-high-frequency (UHF) band of 300 MHz to 3 GHz allow a higher read
range but are easily absorbed by liquids such as water. Frequencies in
the high-frequency (HF) band between 3 MHz to 30 MHz are better able to
penetrate water and other dielectric and lossy materials but have a
shorter read range. The combination of a UHF band antenna with a HF band
antenna allows to use the advantages of each frequency band. Further, a
dual-band antenna allows more flexibility since it can operate in both
frequency bands. However, a challenge in designing dual-band antennas is
to minimize the mutual interference between the individual antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003]The invention will be explained in more detail below using exemplary
embodiments and with the aid of the figures.

[0008]FIG. 5 shows an embodiment of a dual-band antenna with a shorted
loop slot antenna and a spiral antenna.

DETAILED DESCRIPTION OF THE INVENTION

[0009]The invention provides a dual-band antenna comprising a shorted loop
slot antenna and a spiral antenna. The antennas are combined to provide
the advantages of each antenna type. Since the antennas have similar
geometrical structures, the interference between the two antennas is
minimal.

[0010]In an embodiment, the shorted loop slot antenna has a resonance
frequency which is two orders of magnitude higher than a resonance
frequency of the spiral antenna. The ratio of the frequencies of about 1
to 100 can be used to select electric paths by means of capacitors.

[0011]In an embodiment, the shorted loop slot antenna is an
ultra-high-frequency (UHF) band antenna. UHF band antennas have a high
reading range and high data transmission rate.

[0012]In an embodiment, the shorted loop slot antenna has a resonance
frequency lying between 860 MHz and 960 MHz. The frequency range belongs
to the industrial-scientific-medical (ISM) band which can be used for
contactless data transmission, such as in radio frequency identification
tags or contactless smart cards.

[0013]In an embodiment, the spiral antenna is a high-frequency (HF) band
antenna. HF band antennas are less sensitive to the presence of water and
other lossy materials.

[0014]In an embodiment, the spiral antenna has a resonance frequency of
13.56 MHz. The frequency of 13.56 MHz is also in the ISM band and is free
for use.

[0015]In an embodiment, the dual-band antenna comprises a non-conducting
carrier with a top side and a bottom side, metallizations on the top side
of the carrier and metallizations on the bottom side of the carrier. The
shorted loop slot antenna and the spiral antenna are formed in the
metallizations on the carrier.

[0016]In an embodiment, the carrier has a thickness smaller than 100
μm. The carrier is thin enough to be flexible and can be used as a
label for RFID tags for product identification. Further, the thickness
allows capacitors to be implemented using the carrier and the
metallizations on its top and bottom side.

[0017]In an embodiment, the carrier has dimensions smaller than 71
mm×44 mm. The dual-band antenna is thus smaller than a credit card,
which allows for the application of the dual-band antenna to smaller
items.

[0018]In an embodiment, the shorted loop slot antenna comprises an outer
ring and a plate surrounded by the outer ring to form a loop slot in the
metallizations on the top side. The length of the loop slot determines
the frequency of the dual-band antenna and is approximately λ/2,
with λ being the wavelength of the resonance frequency.

[0019]In an embodiment, the plate and the outer ring are electrically
connected. The electrical connection causes a reflection of
electromagnetic waves so that the loop slot acts as a resonator at a
specific frequency.

[0020]In an embodiment, the plate comprises a cut-out to form an inner
loop. The cut-out in the plate is necessary to allow a magnetic flux to
pass through a spiral antenna arranged outside the shorted loop slot
antenna without blocking it by the metallization. Further, the cut-out
reduces eddy currents flowing in the shorted loops of the antenna when
the dual-band antenna is subjected to HF-frequencies.

[0021]In an embodiment, a bypass strip couples a side of the inner ring to
an opposite side of the inner ring. The bypass strip conducts surface
currents which were previously present in the plate without the cut-out
and preserves the shorted loop slot antenna characteristics.

[0022]In an embodiment, the bypass strip is coupled by means of capacitors
which conduct at ultra-high-frequencies (UHF) and do not conduct at
high-frequencies (HF). The capacitors comprise a first metallization on
the bottom side of the carrier which extends at least over the
metallization of one side of the inner ring to the metallization of the
opposite side of the inner ring.

[0023]In an embodiment, the inner ring comprises a non-conducting gap
cutting through the inner ring.

[0024]In an embodiment, the dual-band antenna comprises a second
metallization on the bottom side of the carrier which extends at least
across the gap of the inner ring. The second metallization, the carrier
and the metallization on each side of the gap in the inner ring form two
capacitors. Each capacitor has a capacitance so that
ultra-high-frequencies (UHF) are conducted and high-frequencies (HF) are
not conducted across the gap in the inner ring.

[0025]In an embodiment, the outer ring comprises a non-conducting gap
cutting through the outer ring.

[0026]In an embodiment, the dual-band antenna comprises a third
metallization on the bottom side of the carrier which extends at least
across the gap in the outer ring. The third metallization, the carrier
and the metallization on each side of the gap in the outer ring form two
capacitors, each having a capacitance so that ultra-high-frequencies
(UHF) are conducted and high-frequencies (HF) are not conducted across
the gap in the outer ring. The first, second and third metallization
together with the gaps in the inner and outer ring are used for combining
the high-frequency (HF) spiral antenna with the ultra-high-frequency
(UHF) shorted loop slot antenna. The resulting capacitors conduct only at
ultra-high-frequencies (UHF) and present an open circuit for
high-frequencies (HF) so that the inner and outer ring of the shorted
loop slot antenna can be used as two turns of conductors for the spiral
antenna without affecting the shorted loop slot antenna characteristic.

[0027]In an embodiment, the resonance frequency of the shorted loop slot
antenna is determined by the loop slot length. The resonance frequency
can be chosen to be, for example, 868 MHz.

[0028]In an embodiment, the input impedance of the shorted loop slot
antenna is determined by the loop slot length. Since an electronic chip
is usually capacitive, it is necessary for the shorted loop slot antenna
to have an inductive behavior in order to achieve power matching. This is
achieved by setting the resonance frequency of the shorted loop slot
antenna above the desired working frequency.

[0029]In an embodiment, the input impedance of the shorted loop slot
antenna is determined by a feed position along the loop slot. The feed
position is a position along the loop slot at which an electronic chip is
connected to the antenna. By varying the position at which the electronic
chip is connected to, the input impedance can be adjusted.

[0030]In an embodiment, the input impedance of the shorted loop slot
antenna is determined by a width of the loop slot.

[0031]In an embodiment, the spiral antenna is formed in the metallization
on the top side and comprises turns of conductor arranged around the
outer ring of the shorted loop slot antenna or comprises turns of
conductor arranged inside the inner ring of the shorted loop slot
antenna. Since the spiral antenna consists of loops of conductors and the
outer ring as well as the inner ring also are in the form of loops, only
minimal interference between the spiral antenna and the shorted loop slot
antenna occurs. The spiral antenna is placed outside the shorted loop
slot antenna so that the area through which magnetic flux passes is
maximal. If it is placed inside the shorted loop slot antenna the size of
the dual-band antenna can be further reduced.

[0032]In an embodiment, additional turns of conductor for the spiral
antenna comprise the outer ring and the inner ring of the shorted loop
slot antenna. The outer ring and the inner ring of the shorted loop slot
antenna are thus reused as additional turns for the spiral antenna. The
coupling and decoupling of the inner ring and the outer ring is achieved
by providing capacitors which conduct at ultra-high-frequencies (UHF) and
do not conduct at high-frequencies (HF).

[0033]In an embodiment, the resonance frequency of the spiral antenna is
determined by the number of conductor turns of the spiral antenna. The
resonance frequency is given by the inductance and the capacitance of the
spiral antenna. The inductance increases with the number of conductor
turns.

[0034]In an embodiment, the antenna comprises fourth and fifth
metallizations on the bottom side of the carrier for altering the
capacitance of the spiral antenna to tune the center frequency of the
spiral antenna.

[0035]In an embodiment, a quality factor of the spiral antenna is
determined by the conductor width of its conductor turns. A smaller
conductor width leads to higher losses and to a lower quality factor. The
wider bandwidth associated with a lower quality factor provides practical
robustness to detuning effects.

[0036]In an embodiment, an electronic chip is coupled in parallel to the
shorted loop slot antenna and the spiral antenna. The electronic chip
connected to the dual-band antenna thus only requires one connection and
no switching between the high-frequency and ultra-high-frequency antenna
is necessary.

[0037]In an embodiment, the electronic chip is coupled to the inner ring
and the outer ring. The electronic chip can thus be supplied with
electrical power by the shorted loop slot antenna.

[0038]In an embodiment, the electronic chip is electrically connected to
sixth and seventh metallizations on the bottom side of the carrier.

[0039]In an embodiment, the first metallization, the second metallization,
the fourth metallization and the sixth metallization are electrically
connected.

[0040]In an embodiment, the third metallization, the fifth metallization
and the seventh metallization are electrically connected. Since the
first, second, third, fourth, fifth, sixth and seventh metallizations
perform a similar function that is to provide a capacitance, they can be
combined to form single metal pads.

[0041]In an embodiment, the electronic chip is electrically connected to
the inner ring by means of a first via. The inner ring is not only
connected to the shorted loop slot antenna but also forms a turn of the
spiral antenna so that the chip can also be supplied by the spiral
antenna.

[0042]In an embodiment, the electronic chip is electrically connected to
an outermost turn of the spiral antenna by means of a second via.

[0043]In an embodiment, at least one of the inner ring, the outer ring and
the turns of conductors have a rectangular, circular or elliptical shape.

[0044]The invention further provides for the use of the dual-band antenna
in a contactless data storage medium. The power supply and the data
transfer can thus be achieved contactlessly in two different frequency
bands.

[0045]In an embodiment, the contactless data storage medium is a radio
frequency identification tag or a smart card.

[0046]FIG. 1 shows an embodiment of a shorted loop slot antenna 1,
comprising a conducting outer ring 9 and a conducting plate 10. A loop
slot 12 is formed between the outer ring 9 and the plate 10. The length
of the loop slot 12 determines the resonance frequency of the shorted
loop slot antenna 1 and is approximately λ/2, where λ is the
wavelength of the resonance frequency. A short 11 electrically connects
the outer ring 9 to the plate 10 imposing boundary conditions on the
electromagnetic waves in the loop slot 12 so that a resonator is
achieved. An electronic chip 4 is connected with one terminal to the
plate 10 and with the other terminal to the outer ring 9. To achieve
power matching, the feed position F of the electronic chip 4 and the
width W of the loop slot 12 can be adjusted. Further, since the
electronic chip 4 usually shows capacitive behavior, the loop slot length
can be decreased so that the antenna 1 shows a slightly increased
resonance frequency with inductive behavior.

[0047]FIG. 2 shows a modified embodiment of the shorted loop slot antenna
1 of FIG. 1. Same reference signs refer to the same features and will not
be described again. The large conducting plate 10 in FIG. 1 prevents
magnetic flux flowing through a spiral antenna 2, which is shown in FIG.
5. Further, the spiral antenna 2 causes eddy currents to flow inside the
plate 10. A cut-out 16 from the metal plate 10 reduces the eddy currents
and allows more flux to flow through the spiral antenna 2. The plate 10
with the cut-out 16 forms an inner ring 17. A bypass strip 18 from one
side 19 of the inner ring to an opposite side 20 of the inner ring is
provided to allow surface currents present in the plate 10 at UHF
frequencies to flow in order to preserve the shorted loop slot antenna
characteristic.

[0048]FIG. 3 shows an embodiment that is based on a modification of the
shorted loop slot antenna in FIG. 2. The embodiment allows combination of
the shorted loop slot antenna 1 and the spiral antenna 2 and increases
the efficiency of the spiral antenna 2. When HF frequencies are applied
to the spiral antenna 2, currents are induced in the inner ring 17 and
the outer ring 9 which push the magnetic field to the outside and so
reduce the magnetic flux in the spiral antenna 2. Further, it is desired
to reuse the inner ring 17 and the outer ring 9 as additional turns of
the spiral antenna 2.

[0049]To achieve the above goal, the inner ring 17 and the outer ring 9
are provided with non-conducting gaps 23 and 26, respectively. The
shorted loop slot antenna 1 is formed in metallizations on the top side 6
of a carrier 5. On a bottom side 7 of the carrier 5, a second
metallization 24 and a third metallization 27 are provided which
respectively extend across the gap 23 in the inner ring 17 and the gap 26
in the outer ring 9. Similarly, the bypass strip 18 of the FIG. 2 is no
longer electrically connected to the side 19 and the opposite side 20 of
the inner ring 17 but is formed as a first metallization 22 on the bottom
side 7 of the carrier 5. The metallizations on the bottom side of the
carrier are shown with dotted lines.

[0050]The first metallization 21, the second metallization 24, and the
third metallization 27 on the bottom side 7 and the inner ring 17 and the
outer ring 9 on the top side 6 of the carrier 5 form capacitor pairs 21,
25 and 28. The shorted loop slot antenna 1 is designed to operate in the
ultra-high-frequency (UHF) range while the spiral antenna 2 is designed
for use in the high-frequency (HF) range. The operation frequencies of
the two antennas 1, 2 differ from each other by two orders of magnitude.
It is therefore possible to use capacitors which conduct at the
ultra-high-frequency (UHF) and do not conduct at the high-frequency (HF).
The terms "conduct" and "non-conduct" are used in a relative sense to
each other, as a capacitor usually conducts any alternating currents. If
the frequencies are related to each other by a ratio of 1:100, then the
conductance of the capacitor at the higher frequency is 100% while at the
lower frequency it is relatively non-conductive at 1%.

[0051]At ultra-high-frequencies (UHF), the capacitors 21, 25 and 28
conduct currents so that the shorted loop slot antenna 1 in FIG. 3
functions in the same way as the shorted loop slot antenna 1 of FIG. 2 by
shorting the gap 23 in the inner ring and the gap 26 in the outer ring,
as well as coupling the bypass strip from the side 19 of the inner ring
17 to the opposite side 20 of the inner ring. At high-frequencies (HF),
the capacitors 21, 25 and 28 do not conduct so that the outer ring 9 and
the inner ring 17 can be used as additional turns of conductors for the
spiral antenna 2, as is described together with FIG. 5.

[0052]FIG. 4 is used to illustrate the capacitors 25 and 28 in the inner
ring 17 and the outer ring 9 of FIG. 3. A carrier 5 has a top side 6 and
a bottom side 7 which are provided with metallizations. For the inner
ring capacitor 25, the top side metallization is the inner ring 17 which
is opened by a non-conducting gap 23, while the bottom side metallization
is the second metallization 24. For the outer ring capacitor 28, the top
metallization is the outer ring 9 with a non-conducting gap 26 cutting
through the outer ring 9 and the bottom metallization is the third
metallization 27. The metallizations on the top and the bottom side 6, 7
of the carrier 5 form parallel plate capacitors. The capacitors are
dimensioned such that ultra-high-frequencies (UHF) are passed through
them and high-frequencies (HF) are blocked. At ultra-high-frequencies
(UHF), currents flow from the left top metallization 9, 17 through the
carrier 5 to the bottom metallization 24, 27 and back through the carrier
5 to the right top metallization 9, 17. The function of the gaps 23 and
26 are thus bypassed by the capacitors 25 and 28 at
ultra-high-frequencies (UHF). The dimensioning of the capacitors is
influenced by the area of the metallizations on the top side 6 and the
bottom side 7, the distance between the metallizations on the top side 6
and the bottom side 7 and the electric permittivity of the carrier 5. As
an example, the thickness of the carrier 5 is chosen to be 25 μm and
the material is a polyimide, such as ESPANEX MB FRG-Z. A person skilled
in the art knows how to adjust the dimensions of the first, second and
third metallizations 22, 24 and 27 and to determine the thickness of the
carrier 5 and is able to use different materials for the carrier 5 in
order to achieve the desired capacitances of the capacitors 21, 25 and
28. FIGS. 3 and 5 show different dimensions of the first, second and
third metallizations 21, 24 and 27 as an illustration. The capacitive
coupling using the first metallization 22 for the bypass strip is
achieved in a similar manner as described above.

[0053]FIG. 5 shows an embodiment of the dual-band antenna comprising a
shorted loop slot antenna 1 and a spiral antenna 2. The shorted loop slot
antenna 1 is the same as shown in FIG. 3 with additional modifications to
the metallizations on the bottom layer 7. The spiral antenna 2 consists
of turns of conductors 29 which are arranged in a spiral manner, starting
from an outermost conductor turn 30 and ending at an innermost conductor
turn 31. The spiral antenna 2 has a start 37 at the outermost conductor
30 and an end 38 at the innermost conductor 31 at which the induced
voltage can be accessed. The number of conductor turns 29 shown is three.
However, a different number of conductor turns 29 may be used. The number
of conductor turns 29 determines the resonance frequency of the spiral
antenna 2 and give it an inductive behavior. More conductor turns 29 lead
to a higher induced voltage in the spiral antenna 2. The width C of the
conductor turns 29 can be used to set the quality factor of the spiral
antenna 2. To counter detuning effects, a lower gain and a wider
bandwidth of the spiral antenna 2 can be used. The spiral antenna 2 is
arranged around the shorted loop slot antenna 1 so that more magnetic
flux passes through the conductor turns 29 in order to induce a higher
voltage in the spiral antenna 2. Alternatively, the spiral antenna 2 can
also be arranged inside the inner ring 17 of the shorted loop slot
antenna 1, which reduces the size of the dual-band antenna. The similar
geometrical loop structure of the conductor turns 29 and the rings 9 and
17 leads to minimal mutual interference in the antenna characteristics
when arranging them together on a single carrier 5. The shorted loop slot
antenna 1 and the spiral antenna 2 are shown with rectangular loop
metallizations, which is especially useful when applying the dual-band
antenna to smart cards having a credit card sized carrier. The shorted
loop slot antenna 1 and the spiral antenna 2 can also be designed using
circularly or elliptically shaped metallizations.

[0054]The operation of the dual-band antenna is as follows. At
high-frequencies (HF), for example at 13.56 MHz, the capacitors 21, 25
and 28 are non-conducting so that the gaps 23 in the inner ring and 26 in
the outer ring are not bypassed and the bypass strip is not connected.
The end 38 of the innermost conductor 31 is connected to one end of the
outer ring 9. The other end of the outer ring 9 is connected to one end
of the inner ring 17 by means of the short 11. The other end of the inner
ring 17 is connected to a first via 35 which passes through the carrier 5
to the bottom side 7. A metallization on the bottom side 7 connects the
first via 35 and one terminal of the electronic chip 4. The outer ring 9
and the inner ring 17 thus function as additional conductor turns for the
spiral antenna 2. The start 37 of the outermost conductor turn 30 is
connected to a second via 36 leading through the carrier 5 to a
metallization on the bottom side 7 of the carrier 5 which is connected to
the other terminal of the electronic chip 4. At high-frequencies, the
dual-band antenna acts like a spiral antenna with the number of conductor
turns increased by two due to the inner ring 17 and the outer 9.

[0055]At ultra-high-frequencies (UHF), such as, for example, 868 MHz, the
capacitors 21, 25 and 28 conduct so that the dual-band antenna acts like
the shorted loop slot antenna 1 shown in FIG. 2. In contrast to FIG. 2
the electronic chip 4 is located on the bottom side 7 of the carrier 5.
One terminal of the electronic chip 4 is electrically coupled to the
inner ring 17 and the other terminal to the outer ring 9 by means of
capacitors 39 and 40. The capacitors 39 and 40 are formed by the sixth
and seventh metallizations 41 and 42 on the bottom side 7, the carrier 5
and the metallizations of the inner ring 17 and the outer ring 9 on the
top side 6 and conduct at UHF-frequencies and do not conduct at
HF-frequencies. In principle the electronic chip 4 can also be coupled by
the metallizations 24 and 27 over the gaps but providing extra capacitors
39 and 40 allows choosing the electric chip position independently from
the position of the gap capacitors, for example for the purpose of power
matching of the electronic chip 4 to the shorted loop slot antenna 1. The
start 37 of the outermost conductor turn 30 and the end 38 of the
innermost conductor turn 31 of the spiral antenna 2 are shorted by the
second via 36 and the conducting capacitor between the bottom layer
metallization and the outer ring 9.

[0056]In FIG. 5, the metallizations on the bottom side 7 of the carrier 5
of FIG. 3 have been modified. The first metallization 22 for the bypass
strip is connected to the second metallization 24 of the inner gap
capacitors 25 and to the sixth metallization 41 connected to the
electronic chip 4. Further, the metallization shown in FIG. 5 is larger
as an additional fourth metallization 33 has been added. The fourth
metallization 33 is used to add capacitance to the spiral antenna 2 when
operating at high-frequencies (HF) for adjusting the resonance frequency
of the spiral antenna 2. Similarly, the third metallization 27 of the
outer gap capacitors 28 is connected to the seventh metallization 42
connected to the electronic chip 4 and is combined with a fifth
metallization 34 to add capacitance to the spiral antenna 2 for adjusting
its resonance frequency.

[0057]The dual-band antenna is used to provide a contactless data storage
medium 3 with electrical energy and data. The contactless data storage
medium 3 can be an RFID tag which has an attaching means, such as an
adhesive tape for applying it to a product that is to be identified. The
flexible carrier 5 can be attached to a multitude of differently sized
objects. If the dual-band antenna is used in a smart card, it can be
fixed on a thicker carrier for protection.

[0058]The invention provides for a small and flexible dual-band antenna
which has the advantage of a very low level of interference between the
antennas and allows the reuse of the shorted loop slot antenna 1 as
conductor turns of a spiral antenna 2. The input impedance of both
antennas can be adjusted as well as the quality factor and the resonance
frequency by simple geometric variations in the metallizations.